For recording on recording media such as papers, etc., by writing instruments (e.g., a fountain pen, a felt pen, etc.), there have hitherto been used inks, which are solutions of various dyes dissolved in water or organic solvents.
It is also known that in a so-called ink-jet recording system wherein recording is performed by ejecting a recording liquid in a recording head through discharging orifices by vibration of piezo oscillators, the electrostatic attraction caused by the application of a high voltage, etc., recording liquids obtained by dissolving various dyes in water or organic solvents are used. However, for the ink-jet recording liquid, more stringent performance characteristics are requested than for a general writing ink for writing instruments such as a fountain pen, a felt pen, etc.
In such a recording system recording is performed by ejecting droplets of a recording liquid (a recording ink) onto a recording media. A recording liquid is fundamentally composed of a recording agent (a dye or a pigment) and a liquid medium (water, an organic solvent or a mixture of them) for dissolving or dispersing the recording agent and, if necessary, various additives are added to the recording liquid.
Preferred conditions required for this kind of recording liquid are as follows:
(1) The recording liquid possesses liquid properties (viscosity, surface tension, electric conductivity, etc.) matching the discharging conditions (a driving voltage and a driving frequency of a piezo electric element, the form and material of orifices, the diameter of orifices, etc.), PA1 (2) The recording liquid can be stored for a long period of time and does not cause clogging of orifices during use. PA1 (3) The recording liquid is quickly fixed onto recording media such as papers, films, etc., the outlines of the resulting ink dots are smooth, and blotting of the dotted ink is minimized. PA1 (4) the recorded image of the recording liquid has a clear color tone and a high density. PA1 (5) The recorded image of the recording liquid has excellent water resistance and light resistance. PA1 (6) The recording liquid does not attack or erode surrounding materials (the container for the recording liquid, connecting tubes for discharging orifices, sealants, etc.) PA1 (7) The recording liquid has no unpleasant smell, toxicity, inflammability, etc.
As this kind of recording liquid, there are known solutions or dispersions of various dyes or pigments in aqueous or nonaqueous solvents as disclosed, for example, in Japanese Patent Publication No. Sho-52-13127, U.S. Pat. Nos. 3,846,141, 3,705,043 and 3,870,528, etc. However, a completely satisfactory recording liquid has not yet been obtained.
As black dyes for use in these recording liquids, following dyes (1) to (6) are known. ##STR3##
However, such known dyes have various problems with stability during storage for a long period of time, clogging of orifies, etc.